Swift 中的单元测试致命错误

Question

如何在 Swift 中对 fatalError 代码路径实施单元测试？

例如，我有以下 swift 代码

func divide(x: Float, by y: Float) -> Float {

    guard y != 0 else {
        fatalError("Zero division")
    }

    return x / y
}

我想在 y = 0 时对案例进行单元测试。

注意，我想使用 fatalError 而不是任何其他断言函数。

Answer 1

这个想法是用你自己的函数替换内置的 fatalError 函数，它在单元测试执行期间被替换，这样你就可以在其中运行单元测试断言。

然而，棘手的部分是 fatalError 是 @noreturn，所以你需要用一个永远不会 returns.

的函数来覆盖它

覆盖致命错误

仅在您的应用目标中（不要添加到单元测试目标）：

// overrides Swift global `fatalError`
@noreturn func fatalError(@autoclosure message: () -> String = "", file: StaticString = __FILE__, line: UInt = __LINE__) {
    FatalErrorUtil.fatalErrorClosure(message(), file, line)
    unreachable()
}

/// This is a `noreturn` function that pauses forever
@noreturn func unreachable() {
    repeat {
        NSRunLoop.currentRunLoop().run()
    } while (true)
}

/// Utility functions that can replace and restore the `fatalError` global function.
struct FatalErrorUtil {

    // Called by the custom implementation of `fatalError`.
    static var fatalErrorClosure: (String, StaticString, UInt) -> () = defaultFatalErrorClosure

    // backup of the original Swift `fatalError`
    private static let defaultFatalErrorClosure = { Swift.fatalError([=10=], file: , line: ) }

    /// Replace the `fatalError` global function with something else.
    static func replaceFatalError(closure: (String, StaticString, UInt) -> ()) {
        fatalErrorClosure = closure
    }

    /// Restore the `fatalError` global function back to the original Swift implementation
    static func restoreFatalError() {
        fatalErrorClosure = defaultFatalErrorClosure
    }
}

分机

将以下扩展添加到您的单元测试目标：

extension XCTestCase {
    func expectFatalError(expectedMessage: String, testcase: () -> Void) {

        // arrange
        let expectation = expectationWithDescription("expectingFatalError")
        var assertionMessage: String? = nil

        // override fatalError. This will pause forever when fatalError is called.
        FatalErrorUtil.replaceFatalError { message, _, _ in
            assertionMessage = message
            expectation.fulfill()
        }

        // act, perform on separate thead because a call to fatalError pauses forever
        dispatch_async(dispatch_get_global_queue(QOS_CLASS_USER_INITIATED, 0), testcase)

        waitForExpectationsWithTimeout(0.1) { _ in
            // assert
            XCTAssertEqual(assertionMessage, expectedMessage)

            // clean up 
            FatalErrorUtil.restoreFatalError()
        }
    }
}

测试用例

class TestCase: XCTestCase {
    func testExpectPreconditionFailure() {
        expectFatalError("boom!") {
            doSomethingThatCallsFatalError()
        }
    }
}

我从这个 post 中得到关于单元测试 assert 和 precondition 的想法： Testing assertion in Swift

Answer 2

感谢 nschum and Ken Ko 这个答案背后的想法。

Here is a gist for how to do it.

Here is an example project.

这个答案不仅仅针对致命错误。它也适用于其他断言方法（assert、assertionFailure、precondition、preconditionFailure 和 fatalError）

1。将 `ProgrammerAssertions.swift` 拖放到您的应用程序或被测框架的目标中。就在你的源代码旁边。

ProgrammerAssertions.swift

import Foundation

/// drop-in replacements

public func assert(@autoclosure condition: () -> Bool, @autoclosure _ message: () -> String = "", file: StaticString = __FILE__, line: UInt = __LINE__) {
    Assertions.assertClosure(condition(), message(), file, line)
}

public func assertionFailure(@autoclosure message: () -> String = "", file: StaticString = __FILE__, line: UInt = __LINE__) {
    Assertions.assertionFailureClosure(message(), file, line)
}

public func precondition(@autoclosure condition: () -> Bool, @autoclosure _ message: () -> String = "", file: StaticString = __FILE__, line: UInt = __LINE__) {
    Assertions.preconditionClosure(condition(), message(), file, line)
}

@noreturn public func preconditionFailure(@autoclosure message: () -> String = "", file: StaticString = __FILE__, line: UInt = __LINE__) {
    Assertions.preconditionFailureClosure(message(), file, line)
    runForever()
}

@noreturn public func fatalError(@autoclosure message: () -> String = "", file: StaticString = __FILE__, line: UInt = __LINE__) {
    Assertions.fatalErrorClosure(message(), file, line)
    runForever()
}

/// Stores custom assertions closures, by default it points to Swift functions. But test target can override them.
public class Assertions {

    public static var assertClosure              = swiftAssertClosure
    public static var assertionFailureClosure    = swiftAssertionFailureClosure
    public static var preconditionClosure        = swiftPreconditionClosure
    public static var preconditionFailureClosure = swiftPreconditionFailureClosure
    public static var fatalErrorClosure          = swiftFatalErrorClosure

    public static let swiftAssertClosure              = { Swift.assert([=10=], , file: , line: ) }
    public static let swiftAssertionFailureClosure    = { Swift.assertionFailure([=10=], file: , line: ) }
    public static let swiftPreconditionClosure        = { Swift.precondition([=10=], , file: , line: ) }
    public static let swiftPreconditionFailureClosure = { Swift.preconditionFailure([=10=], file: , line: ) }
    public static let swiftFatalErrorClosure          = { Swift.fatalError([=10=], file: , line: ) }
}

/// This is a `noreturn` function that runs forever and doesn't return.
/// Used by assertions with `@noreturn`.
@noreturn private func runForever() {
    repeat {
        NSRunLoop.currentRunLoop().run()
    } while (true)
}

2。将 `XCTestCase+ProgrammerAssertions.swift` 拖放到您的测试目标。除了你的测试用例。

XCTestCase+ProgrammerAssertions.swift

import Foundation
import XCTest
@testable import Assertions

private let noReturnFailureWaitTime = 0.1

public extension XCTestCase {

    /**
     Expects an `assert` to be called with a false condition.
     If `assert` not called or the assert's condition is true, the test case will fail.

     - parameter expectedMessage: The expected message to be asserted to the one passed to the `assert`. If nil, then ignored.
     - parameter file:            The file name that called the method.
     - parameter line:            The line number that called the method.
     - parameter testCase:        The test case to be executed that expected to fire the assertion method.
     */
    public func expectAssert(
        expectedMessage: String? = nil,
        file: StaticString = __FILE__,
        line: UInt = __LINE__,
        testCase: () -> Void
        ) {

            expectAssertionReturnFunction("assert", file: file, line: line, function: { (caller) -> () in

                Assertions.assertClosure = { condition, message, _, _ in
                    caller(condition, message)
                }

                }, expectedMessage: expectedMessage, testCase: testCase) { () -> () in
                    Assertions.assertClosure = Assertions.swiftAssertClosure
            }
    }

    /**
     Expects an `assertionFailure` to be called.
     If `assertionFailure` not called, the test case will fail.

     - parameter expectedMessage: The expected message to be asserted to the one passed to the `assertionFailure`. If nil, then ignored.
     - parameter file:            The file name that called the method.
     - parameter line:            The line number that called the method.
     - parameter testCase:        The test case to be executed that expected to fire the assertion method.
     */
    public func expectAssertionFailure(
        expectedMessage: String? = nil,
        file: StaticString = __FILE__,
        line: UInt = __LINE__,
        testCase: () -> Void
        ) {

            expectAssertionReturnFunction("assertionFailure", file: file, line: line, function: { (caller) -> () in

                Assertions.assertionFailureClosure = { message, _, _ in
                    caller(false, message)
                }

                }, expectedMessage: expectedMessage, testCase: testCase) { () -> () in
                    Assertions.assertionFailureClosure = Assertions.swiftAssertionFailureClosure
            }
    }

    /**
     Expects an `precondition` to be called with a false condition.
     If `precondition` not called or the precondition's condition is true, the test case will fail.

     - parameter expectedMessage: The expected message to be asserted to the one passed to the `precondition`. If nil, then ignored.
     - parameter file:            The file name that called the method.
     - parameter line:            The line number that called the method.
     - parameter testCase:        The test case to be executed that expected to fire the assertion method.
     */
    public func expectPrecondition(
        expectedMessage: String? = nil,
        file: StaticString = __FILE__,
        line: UInt = __LINE__,
        testCase: () -> Void
        ) {

            expectAssertionReturnFunction("precondition", file: file, line: line, function: { (caller) -> () in

                Assertions.preconditionClosure = { condition, message, _, _ in
                    caller(condition, message)
                }

                }, expectedMessage: expectedMessage, testCase: testCase) { () -> () in
                    Assertions.preconditionClosure = Assertions.swiftPreconditionClosure
            }
    }

    /**
     Expects an `preconditionFailure` to be called.
     If `preconditionFailure` not called, the test case will fail.

     - parameter expectedMessage: The expected message to be asserted to the one passed to the `preconditionFailure`. If nil, then ignored.
     - parameter file:            The file name that called the method.
     - parameter line:            The line number that called the method.
     - parameter testCase:        The test case to be executed that expected to fire the assertion method.
     */
    public func expectPreconditionFailure(
        expectedMessage: String? = nil,
        file: StaticString = __FILE__,
        line: UInt = __LINE__,
        testCase: () -> Void
        ) {

            expectAssertionNoReturnFunction("preconditionFailure", file: file, line: line, function: { (caller) -> () in

                Assertions.preconditionFailureClosure = { message, _, _ in
                    caller(message)
                }

                }, expectedMessage: expectedMessage, testCase: testCase) { () -> () in
                    Assertions.preconditionFailureClosure = Assertions.swiftPreconditionFailureClosure
            }
    }

    /**
     Expects an `fatalError` to be called.
     If `fatalError` not called, the test case will fail.

     - parameter expectedMessage: The expected message to be asserted to the one passed to the `fatalError`. If nil, then ignored.
     - parameter file:            The file name that called the method.
     - parameter line:            The line number that called the method.
     - parameter testCase:        The test case to be executed that expected to fire the assertion method.
     */
    public func expectFatalError(
        expectedMessage: String? = nil,
        file: StaticString = __FILE__,
        line: UInt = __LINE__,
        testCase: () -> Void) {

            expectAssertionNoReturnFunction("fatalError", file: file, line: line, function: { (caller) -> () in

                Assertions.fatalErrorClosure = { message, _, _ in
                    caller(message)
                }

                }, expectedMessage: expectedMessage, testCase: testCase) { () -> () in
                    Assertions.fatalErrorClosure = Assertions.swiftFatalErrorClosure
            }
    }

    // MARK:- Private Methods

    private func expectAssertionReturnFunction(
        functionName: String,
        file: StaticString,
        line: UInt,
        function: (caller: (Bool, String) -> Void) -> Void,
        expectedMessage: String? = nil,
        testCase: () -> Void,
        cleanUp: () -> ()
        ) {

            let expectation = expectationWithDescription(functionName + "-Expectation")
            var assertion: (condition: Bool, message: String)? = nil

            function { (condition, message) -> Void in
                assertion = (condition, message)
                expectation.fulfill()
            }

            // perform on the same thread since it will return
            testCase()

            waitForExpectationsWithTimeout(0) { _ in

                defer {
                    // clean up
                    cleanUp()
                }

                guard let assertion = assertion else {
                    XCTFail(functionName + " is expected to be called.", file: file.stringValue, line: line)
                    return
                }

                XCTAssertFalse(assertion.condition, functionName + " condition expected to be false", file: file.stringValue, line: line)

                if let expectedMessage = expectedMessage {
                    // assert only if not nil
                    XCTAssertEqual(assertion.message, expectedMessage, functionName + " called with incorrect message.", file: file.stringValue, line: line)
                }
            }
    }

    private func expectAssertionNoReturnFunction(
        functionName: String,
        file: StaticString,
        line: UInt,
        function: (caller: (String) -> Void) -> Void,
        expectedMessage: String? = nil,
        testCase: () -> Void,
        cleanUp: () -> ()
        ) {

            let expectation = expectationWithDescription(functionName + "-Expectation")
            var assertionMessage: String? = nil

            function { (message) -> Void in
                assertionMessage = message
                expectation.fulfill()
            }

            // act, perform on separate thead because a call to function runs forever
            dispatch_async(dispatch_get_global_queue(QOS_CLASS_USER_INITIATED, 0), testCase)

            waitForExpectationsWithTimeout(noReturnFailureWaitTime) { _ in

                defer {
                    // clean up
                    cleanUp()
                }

                guard let assertionMessage = assertionMessage else {
                    XCTFail(functionName + " is expected to be called.", file: file.stringValue, line: line)
                    return
                }

                if let expectedMessage = expectedMessage {
                    // assert only if not nil
                    XCTAssertEqual(assertionMessage, expectedMessage, functionName + " called with incorrect message.", file: file.stringValue, line: line)
                }
            }
    }
}

3。像往常一样正常使用 `assert`、`assertionFailure`、`precondition`、`preconditionFailure` 和 `fatalError`。

例如：如果您有一个像下面这样进行除法的函数：

func divideFatalError(x: Float, by y: Float) -> Float {

    guard y != 0 else {
        fatalError("Zero division")
    }

    return x / y
}

4。使用新方法 `expectAssert`、`expectAssertionFailure`、`expectPrecondition`、`expectPreconditionFailure` 和 `expectFatalError`.

对它们进行单元测试

你可以用下面的代码测试0分区。

func testFatalCorrectMessage() {
    expectFatalError("Zero division") {
        divideFatalError(1, by: 0)
    }
}

或者，如果您不想测试消息，您可以直接测试。

func testFatalErrorNoMessage() {
    expectFatalError() {
        divideFatalError(1, by: 0)
    }
}

Answer 3

Swift 4 和 Swift 3

基于 Ken 的回答。

在您的 App Target 中添加以下内容：

import Foundation

// overrides Swift global `fatalError`
public func fatalError(_ message: @autoclosure () -> String = "", file: StaticString = #file, line: UInt = #line) -> Never {
    FatalErrorUtil.fatalErrorClosure(message(), file, line)
    unreachable()
}

/// This is a `noreturn` function that pauses forever
public func unreachable() -> Never {
    repeat {
        RunLoop.current.run()
    } while (true)
}

/// Utility functions that can replace and restore the `fatalError` global function.
public struct FatalErrorUtil {

    // Called by the custom implementation of `fatalError`.
    static var fatalErrorClosure: (String, StaticString, UInt) -> Never = defaultFatalErrorClosure

    // backup of the original Swift `fatalError`
    private static let defaultFatalErrorClosure = { Swift.fatalError([=10=], file: , line: ) }

    /// Replace the `fatalError` global function with something else.
    public static func replaceFatalError(closure: @escaping (String, StaticString, UInt) -> Never) {
        fatalErrorClosure = closure
    }

    /// Restore the `fatalError` global function back to the original Swift implementation
    public static func restoreFatalError() {
        fatalErrorClosure = defaultFatalErrorClosure
    }
}

在您的测试目标中添加以下内容：

import Foundation
import XCTest

extension XCTestCase {
    func expectFatalError(expectedMessage: String, testcase: @escaping () -> Void) {

        // arrange
        let expectation = self.expectation(description: "expectingFatalError")
        var assertionMessage: String? = nil

        // override fatalError. This will pause forever when fatalError is called.
        FatalErrorUtil.replaceFatalError { message, _, _ in
            assertionMessage = message
            expectation.fulfill()
            unreachable()
        }

        // act, perform on separate thead because a call to fatalError pauses forever
        DispatchQueue.global(qos: .userInitiated).async(execute: testcase)

        waitForExpectations(timeout: 0.1) { _ in
            // assert
            XCTAssertEqual(assertionMessage, expectedMessage)

            // clean up
            FatalErrorUtil.restoreFatalError()
        }
    }
}

测试用例：

class TestCase: XCTestCase {
    func testExpectPreconditionFailure() {
        expectFatalError(expectedMessage: "boom!") {
            doSomethingThatCallsFatalError()
        }
    }
}

Answer 4

Nimble ("A Matcher Framework for Swift and Objective-C") 得到你的支持:

Swift Assertions

If you're using Swift, you can use the throwAssertion matcher to check if an assertion is thrown (e.g. fatalError()). This is made possible by @mattgallagher's CwlPreconditionTesting library.

// Swift

// Passes if 'somethingThatThrows()' throws an assertion, 
// such as by calling 'fatalError()' or if a precondition fails:
expect { try somethingThatThrows() }.to(throwAssertion())
expect { () -> Void in fatalError() }.to(throwAssertion())
expect { precondition(false) }.to(throwAssertion())

// Passes if throwing an NSError is not equal to throwing an assertion:
expect { throw NSError(domain: "test", code: 0, userInfo: nil) }.toNot(throwAssertion())

// Passes if the code after the precondition check is not run:
var reachedPoint1 = false
var reachedPoint2 = false
expect {
    reachedPoint1 = true
    precondition(false, "condition message")
    reachedPoint2 = true
}.to(throwAssertion())

expect(reachedPoint1) == true
expect(reachedPoint2) == false

Notes:

This feature is only available in Swift.

It is only supported for x86_64 binaries, meaning you cannot run this matcher on iOS devices, only simulators.

The tvOS simulator is supported, but using a different mechanism, requiring you to turn off the Debug executable scheme setting for your tvOS scheme's Test configuration.

Answer 5

SWIFT 5, 4

此版本不会在每次调用 expectFatalError 时在 GCD 中留下废弃的线程。这通过使用线程而不是 DispatchQueue 来解决。感谢@jedwidz

import Foundation

// overrides Swift global `fatalError`
func fatalError(_ message: @autoclosure () -> String = String(), file: StaticString = #file, line: UInt = #line) -> Never {
    FatalErrorUtil.fatalErrorClosure(message(), file, line)
}

/// Utility functions that can replace and restore the `fatalError` global function.
enum FatalErrorUtil {
    typealias FatalErrorClosureType = (String, StaticString, UInt) -> Never
    // Called by the custom implementation of `fatalError`.
    static var fatalErrorClosure: FatalErrorClosureType = defaultFatalErrorClosure
    
    // backup of the original Swift `fatalError`
    private static let defaultFatalErrorClosure: FatalErrorClosureType = { Swift.fatalError([=10=], file: , line: ) }
    
    /// Replace the `fatalError` global function with something else.
    static func replaceFatalError(closure: @escaping FatalErrorClosureType) {
        fatalErrorClosure = closure
    }
    
    /// Restore the `fatalError` global function back to the original Swift implementation
    static func restoreFatalError() {
        fatalErrorClosure = defaultFatalErrorClosure
    }
}

import XCTest
@testable import TargetName

extension XCTestCase {
    func expectFatalError(expectedMessage: String, testcase: @escaping () -> Void) {

        // arrange
        let expectation = self.expectation(description: "expectingFatalError")
        var assertionMessage: String? = nil

        // override fatalError. This will terminate thread when fatalError is called.
        FatalErrorUtil.replaceFatalError { message, _, _ in
            DispatchQueue.main.async {
                assertionMessage = message
                expectation.fulfill()
            }
            // Terminate the current thread after expectation fulfill
            Thread.exit()
            // Since current thread was terminated this code never be executed
            fatalError("It will never be executed")
        }

        // act, perform on separate thread to be able terminate this thread after expectation fulfill
        Thread(block: testcase).start()
        
        waitForExpectations(timeout: 0.1) { _ in
            // assert
            XCTAssertEqual(assertionMessage, expectedMessage)

            // clean up
            FatalErrorUtil.restoreFatalError()
        }
    }
}

class TestCase: XCTestCase {
    func testExpectPreconditionFailure() {
        expectFatalError(expectedMessage: "boom!") {
            doSomethingThatCallsFatalError()
        }
    }
}

Swift 中的单元测试致命错误

Unit Test fatalError in Swift

unit-testing

fatal-error

ios

xctest

swift

覆盖致命错误

分机

测试用例

1。将 `ProgrammerAssertions.swift` 拖放到您的应用程序或被测框架的目标中。就在你的源代码旁边。

2。将 `XCTestCase+ProgrammerAssertions.swift` 拖放到您的测试目标。除了你的测试用例。

3。像往常一样正常使用 `assert`、`assertionFailure`、`precondition`、`preconditionFailure` 和 `fatalError`。

4。使用新方法 `expectAssert`、`expectAssertionFailure`、`expectPrecondition`、`expectPreconditionFailure` 和 `expectFatalError`.

Swift 4 和 Swift 3

Swift 中的单元测试致命错误

Unit Test fatalError in Swift

unit-testing

fatal-error

ios

xctest

swift

覆盖致命错误

分机

测试用例

1。将 ProgrammerAssertions.swift 拖放到您的应用程序或被测框架的目标中。就在你的源代码旁边。

2。将 XCTestCase+ProgrammerAssertions.swift 拖放到您的测试目标。除了你的测试用例。

3。像往常一样正常使用 assert、assertionFailure、precondition、preconditionFailure 和 fatalError。

4。使用新方法 expectAssert、expectAssertionFailure、expectPrecondition、expectPreconditionFailure 和 expectFatalError.

Swift 4 和 Swift 3

1。将 `ProgrammerAssertions.swift` 拖放到您的应用程序或被测框架的目标中。就在你的源代码旁边。

2。将 `XCTestCase+ProgrammerAssertions.swift` 拖放到您的测试目标。除了你的测试用例。

3。像往常一样正常使用 `assert`、`assertionFailure`、`precondition`、`preconditionFailure` 和 `fatalError`。

4。使用新方法 `expectAssert`、`expectAssertionFailure`、`expectPrecondition`、`expectPreconditionFailure` 和 `expectFatalError`.